1. Field of the Invention
The invention relates to a fuel injection apparatus and a fuel injection control method for an internal combustion engine. More particularly, the invention relates to a fuel injection apparatus and a fuel injection control method for a dual injection type internal combustion engine which includes an injector for cylinder injection that injects fuel into a cylinder, and an injector for intake port injection that injects fuel into an intake port.
2. Description of the Related Art
A dual injection type internal combustion engine is known which includes an injector for cylinder injection that injects fuel into a cylinder and an injector for intake port injection that injects fuel into an intake port. In this dual injection type internal combustion engine, one of these injectors is selected and used depending on an operation region of an engine, stratified combustion or homogenous combustion is performed, and both of the injectors are used in a predetermined operation region.
As an example of a fuel injection apparatus for such a dual injection type internal combustion engine, Japanese Patent Laid-Open Publication No. 10-103118 discloses a fuel injection apparatus which includes an injector for intake port injection and an injector for cylinder injection. This fuel injection apparatus suppresses fluctuation of an air-fuel ratio, which occurs when the injector is changed, by setting the ratio of an amount of fuel to be injected into the cylinder in consideration of a time lag of fuel supply by port injection.
However, Japanese Patent Laid-Open Publication No. 10-103118 discloses only that the fuel injection apparatus appropriately sets an amount of fuel injected from the injector for cylinder injection and an amount of fuel injected from the injector for intake port injection in order to suppress fluctuation of an air-fuel ratio which occurs when the fuel injection injector is changed. There is no description concerning fuel injection timing in Japanese Patent Laid-Open Publication No. 10-103118.
In a dual injection type internal combustion engine in which the combustion mode is changed depending on an operation region, for example, in an engine in which the combustion mode is changed to the stratified lean combustion mode, the homogeneous lean combustion mode, the homogeneous stoichiometric combustion mode, or the like, basically, fuel is injected from only one of an injector for cylinder injection and an injector for intake port injection. In this case, it is considerably important how to set the fuel injection timing. When a request to change the combustion mode, that is, a request to change the fuel injector is made due to transition of the operation region, fuel injection timing is limited concerning a particular cylinder and the fuel injection timing cannot be set to the requested fuel injection timing, depending on the point of time at which the request to change the combustion mode is made. As a result, the optimum fuel injection mode and the optimum air-fuel ratio cannot be realized, which causes problems such as fluctuation of torque and deterioration of emission.